This invention relates in general to ball nut and screw devices and in particular to an improved structure for diverting the balls contained in such a ball nut and screw device into and out of a ball recirculation tube.
The ball nut and screw device is a well known apparatus which is designed to translate rotary motion of one member into linear motion of another member. A typical ball nut and screw device includes an elongated cylindrical screw which extends through a cylindrical opening formed through a nut. The outer surface of the screw and the inner surface of the nut are formed having complementary helical threads which are generally semi-circular in cross section. However, the outer diameter of the screw is smaller than the inner diameter of the opening formed through the nut. Thus, the outer surface of the screw and the inner surface of the opening formed through the nut do not engage one another. Rather, a plurality of balls are disposed between the screw and the nut. Each of the balls extends partially into both of the complementary threads formed in the screw and the nut so as to provide a rolling engagement therebetween, similar to a ball bearing apparatus.
Typically, the screw is connected to a source of rotational power, while the nut is connected to a load to be moved. By virtue of its connection with the load, the nut is usually restrained from rotating. Thus, when the screw is rotated by the source of rotational power, the nut (and the load connected thereto) are moved axially relative to the screw. Because of the rolling engagement of the balls with the complementary threads of the screw and the nut, such linear movement of the nut is accomplished with very little friction. It will be appreciated that in some applications, it may be desirable to connect the screw to the load to be moved and the nut to the source of rotational power.
However, as the balls roll through the complementary threads of the screw and the nut, they also roll axially therethrough. To accommodate this axial rolling movement of the balls, it is known to provide a mechanism for recirculating the balls from one end of the complementary threads to the other in an endless loop. This ball circulation mechanism typically includes a pair of apertures formed through the nut which extend outwardly from the opposite ends of the complementary threads to the outer surface of the nut. A tube extends across the outer surface of the nut between these two apertures. The tube conducts the balls out the aperture at one end of the nut, across the outer surface thereof, and into the aperture at the other end of the nut to accommodate the rolling axial movement thereof.
It is known to provide some means for facilitating the smooth passage of the recirculating balls into and out of the tube. In one type of ball nut and screw device, the ends of the tube are provided with integral finger portions which extend through the apertures into the area of the complementary threads. The finger portions engage and deflect the balls into and out of the ends of the tube and the complementary threads. While effective, the finger portions of the tube are relatively thin and, thus, subject to breakage. In another type of ball nut and screw device, a deflector body is installed within the complementary threads of the screw and the nut adjacent each of the nut apertures. Each of the deflectors has a surface formed thereon which engages and deflects the balls into and out of the ends of the tube and the complementary threads. Usually, the deflectors are installed from the interior of the nut, with a stud portion extending through a mounting aperture to a threaded fastener provided on the exterior of the nut. This design has improved strength over the tube finger portion design described above, but is more expensive and difficult to install. Thus, it would be desirable to provide an improved mechanism for diverting the balls contained in a ball nut and screw device into and out of a ball recirculation tube which is simple and inexpensive in structure and operation.